| 5 |
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The decay of the top squark depends on the difference between its mass and that of the \lsp\ LSP, |
| 6 |
|
$\Delta m = m_{\tilde{t}}-m_{\lsp}$. If $\Delta m > m_{t}$, the decay $\tilde{t}\to t\lsp$ is expected |
| 7 |
|
to have a large branching fraction. If there is a light chargino \chipm, the decay |
| 8 |
< |
$\tilde{t}\to b\chip\to b W \lsp$ is expected to be significant, especially in the $\Delta m < m_{t}$ region. |
| 8 |
> |
$\tilde{t}\to b\chip\to b W \lsp$ may also be significant, especially in the $\Delta m < m_{t}$ region. |
| 9 |
|
The pair production of top squarks decaying to either of these channels leads to events with two b-jets, two W bosons, |
| 10 |
|
and two LSPs. Our signal thus resembles SM $t\bar{t}$ production but with larger \met\ from |
| 11 |
|
the invisible LSPs. |
| 12 |
< |
We focus on the single lepton final state, which has a significant branching fraction due to the presence of two W bosons |
| 12 |
> |
We focus here on the single lepton final state, which has a significant branching fraction due to the presence of two W bosons |
| 13 |
|
in the final state, |
| 14 |
|
and smaller SM backgrounds than the all-hadronic final state. |
| 15 |
|
%We thus select events with a single lepton and jets and discriminate between |
| 17 |
|
|
| 18 |
|
%\subsection{Event Selection} |
| 19 |
|
|
| 20 |
< |
We require the presence of exactly one well-identified and isolated lepton (e or $\mu$) with transverse |
| 20 |
> |
We require the presence of exactly one well-identified and isolated electron (e) or muon ($\mu$) with transverse |
| 21 |
|
momentum \pt\ $>$ 30 GeV. |
| 22 |
|
We select events with at least four jets with \pt\ $>$ 30 GeV, |
| 23 |
|
which must be well-separated from the selected leptons. |
| 61 |
|
The MC distribution of $n_{jets}$ is reweighted to match the corresponding data distribution, resulting in small corrections of a few \%. |
| 62 |
|
|
| 63 |
|
The SM backgrounds are estimated from events simulated with Monte Carlo (MC) techniques, which are validated and |
| 64 |
< |
(if necessary) corrected using comparisons to data in control regions. The MC expectation is normalized to data in the \mt\ peak region, |
| 64 |
> |
(where necessary) corrected using comparisons to data in control regions. The MC expectation is normalized to data in the \mt\ peak region, |
| 65 |
|
in order to remove systematic uncertainties from integrated luminosity and $t\bar{t}$ cross section, and then extrapolated to the |
| 66 |
|
large \mt\ region. Correction factors and corresponding systematic uncertainties on the MC extrapolation factors are evaluated by |
| 67 |
|
comparing MC to data in dedicated control regions dominated by \wjets\ (obtained by vetoing events with b-jets), \ttll\ |
| 108 |
|
%next-to-leading-logarithmic |
| 109 |
|
%accuracy (NLO+NLL)~\cite{ref:nlonll}. |
| 110 |
|
Our results probe top squarks with masses up to 430 GeV. For comparison, the requirement that SUSY |
| 111 |
< |
provides a natural solution to the hierarchy problem suggests top squarks with masses not exceeding 500--700 GeV~\cite{ref:naturalsusy}. |
| 111 |
> |
provides a natural solution to the hierarchy problem favors top squarks with masses not exceeding 500--700 GeV~\cite{ref:naturalsusy}. |
| 112 |
|
We also interpret our results in the $\tilde{t}\to b\chip\to b W \lsp$ scenario |
| 113 |
|
depicted in Fig.~\ref{fig:diagrams}(b), probing top squarks with masses up to 420 GeV~\cite{ref:stop}. |
| 114 |
|
|
| 115 |
< |
The ATLAS experiment has presented a similar search for top squark pairs~\cite{ref:atlasstop}. |
| 116 |
< |
The constraints from ATLAS on the top squark mass are more stringent than those presented here. The ATLAS model assumes large |
| 117 |
< |
right-handed top quark polarization, while we take the top quark in the $\tilde{t}\to t\lsp$ decay to be unpolarized, |
| 118 |
< |
resulting in a lower signal selection efficiency in our analysis. |
| 115 |
> |
%The ATLAS experiment has presented a similar search for top squark pairs~\cite{ref:atlasstop}. |
| 116 |
> |
%The constraints from ATLAS on the top squark mass are more stringent than those presented here. The ATLAS model assumes large |
| 117 |
> |
%right-handed top quark polarization, while we take the top quark in the $\tilde{t}\to t\lsp$ decay to be unpolarized, |
| 118 |
> |
%resulting in a lower signal selection efficiency in our analysis. |
| 119 |
|
|
| 120 |
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\begin{figure} |
| 121 |
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% Use the relevant command for your figure-insertion program |
